Electromagnetic shielding and an acoustic chamber for a microphone in a mobile electronic device

ABSTRACT

A circuit board in a mobile electronic device has a microphone and related amplifier and signal conditioning circuitry mounted thereon. A radio frequency (RF) shield surrounds and isolates the microphone from electromagnetic interference (EMI). The RF shield together with the circuit board forms an acoustic chamber surrounding the microphone. A hole in the RF shield permits acoustic energy to enter the acoustic chamber and reach the microphone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/852,232 filed on Aug. 6, 2010, said applicationis expressly incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure is related to the field of mobile electronic devices, andmore particularly is related to electromagnetic shielding and audioperformance of an audio system and methods related thereto.

BACKGROUND

Currently, the popularity of mobile communication devices such ascellular telephones, including smartphones and so called superphones,continues to increase as more and more people around the world adoptthem for both personal and business communications. Such mobilecommunication devices enable users to place and receive phone callsalmost anywhere they travel. As the technology incorporated withinmobile communication devices advances, so too has the functionality ofthese devices. Many mobile communication devices provide numerousadvanced features in addition to the basic telephone calling ability.Such features include for example, wireless Internet browsing via acellular data network (e.g., 3G, 4G) or available wireless local areanetwork (WLAN) hotspot, wireless email, calendaring, address book, tasklists, calculators, word processing, spreadsheets, etc. In addition, themore advanced mobile communication devices have the capability ofrunning applications (referred to as ‘apps’) that provide specificfunctionality to the device. Such applications (typically free or lowcost) are downloaded from the Internet and installed on the device.

The increase in the functionality of mobile communication devices isalso driving the demand for smaller and smaller devices that are easierand more convenient for users to carry. This is putting pressure onmobile communication device designers to shrink the physical size ofinternal circuit boards and electrical/electronic components within thedevice. This causes many components to be located closer together,especially the radio frequency (RF) components such as the antenna,microphone components, RF power amplifiers, etc. This increases thepossibility that the various electronic components in the device willsuffer from electromagnetic interference (EMI) either from RF componentsand subsystems in the device and/or from external sources. For example,an internal surface mounted microphone could pick up conducted energydirectly from an RF power amplifier or from the energy radiated by theantenna. This unwanted reception of conducted/near field radiated energyfrom power amplifiers and antennae may be particularly problematic inburst transmission schemes such as a Global System for Mobilecommunications (GSM) system.

Sources of other interfering EMI signals in some mobile wirelesscommunications devices include the liquid crystal display (LCD),microprocessor or central processing unit (CPU), clock generatorcircuits, etc. which radiate RF energy, possibly interfering withunshielded components thereby degrading device performance. Additionalproblems may occur when the conducted and radiated interfering RF energyis coupled to the mobile communications device causing audio breakthrough tests to fail for both the uplink and downlink. Even keyboardcircuits can potentially create unwanted EMI problems. For example, RFreceiver sensitivity is often degraded by the EMI of spectral harmonicsemitted from the microprocessor or CPU via the keyboard because of theresulting loop formed by any keyboard circuits. In some instances,strong RF energy, for example, the transmitted power from the radio viathe antenna interferes with or couples to the microprocessor or CPUinput/output (I/O) lines of the mobile communications device through thekeyboard Key-In and Key-Out lines and causes a reset of themicroprocessor or CPU.

BRIEF DESCRIPTION OF THE DRAWINGS

The mechanism is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a simplified block diagram illustrating several componentblocks of an example handheld wireless mobile communications deviceincorporating the electromagnetically shielded audio system;

FIG. 2 is a diagram illustrating the component features of an examplehandheld wireless mobile communications device incorporating theelectromagnetically shielded audio system;

FIG. 3 is a block diagram illustrating the functional blocks of anexample handheld wireless mobile communications device incorporating theelectromagnetically shielded audio system;

FIG. 4 is an elevational view of a section of an example circuit boardincorporating the electromagnetically shielded audio system;

FIG. 5 is a sectional view of one embodiment of the electromagneticallyshielded audio system;

FIG. 6 is a sectional view of one embodiment of the electromagneticallyshielded audio system;

FIG. 7 is an example layer of a printed circuit board showing themicrophone and surrounding RF shield wall soldering frame;

FIG. 8 is an example layer of a printed circuit board showing the RFshielding plane and balanced microphone signal lines;

FIG. 9 is an example layer of a printed circuit board showing the RFshielding for the balanced microphone signal lines;

FIG. 10 is an example layer of a printed circuit board showing the leftand right balanced signal lines to the microphone amplifier circuit;

FIG. 11 is an example layer of a printed circuit board showing the RFshielding for the left and right balanced signal lines to the microphoneamplifier circuit;

FIG. 12 is an example layer of a printed circuit board showing the RFshielding enclosure soldering frame and microphone amplifier circuitinput signal path;

FIG. 13 is an example layer of a printed circuit board showing the RFshielding for the microphone signal path;

FIG. 14 is an example layer of a printed circuit board showing the rightand left shielded microphone signal lines; and

FIG. 15 is an example layer of a printed circuit board showing theground plane for shielding the microphone signal path.

DETAILED DESCRIPTION Notation Used Throughout

The following notation is used throughout this document:

Term Definition CDMA Code Division Multiple Access CPU CentralProcessing Unit DC Direct Current DSP Digital Signal Processor EDGEEnhanced Data rates for GSM Evolution EMC Electromagnetic CompatibilityEMI Electromagnetic Interference FM Frequency Modulation FPGA FieldProgrammable Gate Array GPRS General Packet Radio Service GPS GlobalPositioning System GSM Global System for Mobile communications ICIntegrated Circuit LAN Local Area Network LCD Liquid Crystal Display MACMedia Access Control PC Personal Computer PCB Printed Circuit Board PCIPeripheral Component Interconnect PCS Personal Communication ServicesPDA Personal Digital Assistant PNA Personal Navigation Assistant RAMRandom Access Memory RAT Radio Access Technology RF Radio Frequency RFIRadio Frequency Interference ROM Read Only Memory RSSI Received SignalStrength Indicator RUIM Re-Usable Identification Module SDIO SecureDigital Input/Output SIM Subscriber Identity Module SPI Serialperipheral interconnect USB Universal Serial Bus WCDMA Wideband CodeDivision Multiple Access WLAN Wireless Local Area Network

DETAILED DESCRIPTION

The present disclosure will now be presented more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the disclosure are shown. The claimed invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout, and prime notation isused to indicate similar elements in alternative embodiments.

The disclosure is directed to providing electromagnetic shielding and anacoustic chamber for a microphone and optionally for components that areelectrically connected to the microphone. The acoustic chamber mayinfluence audio performance of the microphone and therefore of the audiosystem in which the microphone is comprised. For example, the acousticchamber may affect frequency response, voice intelligibility, backgroundnoise rejection, efficiency, signal to noise ratio and sound quality ofthe audio system.

As described above, there may be concerns created when an internalmicrophone, for example, a surface-mounted technology (SMT) microphone,is subjected to EMI from internal or external sources (e.g., poweramplifier, RF subsystem, antenna, digital circuitry, clock circuits,etc.). Concerns related to EMI may be overcome with the electromagneticshielded audio system. The use of an appropriate RF shielding and EMCfilters—in one non-limiting example—reduces audio degradation. In anexample embodiment, a radio frequency (RF) shield surrounds the internalmicrophone and its associated circuitry to reduce or eliminate EMIrelated problems with operation of the microphone. The RF shield mayalso provide adequate isolation from the radiated RF energy emitted bythe antenna during radio transmissions. That is, the RF shield maysubstantially prevent RF energy emitted by the antenna from interactingand/or interfering with the shielded system.

Concerns associated with electromagnetic interference (EMI) in the audiocircuit portion of a communications device such as shown in FIGS. 1, 2and 3 may be addressed by reducing the conducted and radiatedinterfering RF energy that is coupled to the mobile wirelesscommunications device, which otherwise could create audible noise andcause RF immunity failure in both the uplink and downlinkcommunications. An RF shield encloses an EMI filter and microphone toreduce or eliminate the conducted interfering RF energy from thecoupling to the audio circuits via external or internal RF noisesources.

A block diagram illustrating the component features of an examplehandheld wireless mobile communications device incorporating theelectromagnetically shielded audio system is shown in FIG. 1. A diagramillustrating the component features of an example handheld wirelessmobile communications device incorporating the electromagneticallyshielded audio system is shown in FIG. 2.

With reference to FIGS. 1 and 2, the mobile wireless communicationsdevice (e.g., handheld cellular telephone), generally referenced 10, ispresented for illustration purposes only and is a representativenon-limiting example. It is appreciated that the electromagneticallyshielded audio system may be incorporated in numerous other types ofelectronic devices without departing from the scope therefrom.

The device 10 comprises a housing 11 and circuit board 142, such as aconventional printed circuit board (PCB) substrate, for example, securedinside the housing. Note that the term “circuit board” as used hereinrefers to any dielectric substrate, PCB, ceramic substrate or othercircuit carrying structure for carrying signal circuits and electroniccomponents within the mobile wireless communications device 10. Further,the term circuit board, although used in the singular, may also refer toa plurality of circuit boards. In this example, the housing 11 comprisesa static housing, for example, as opposed to a flip or sliding housingwhich are used in many cellular telephones. These and other housingconfigurations, however, may also be used.

Analog and digital circuitry 148, mounted on circuit board 142, maycomprise a microprocessor, memory, one or more broadband and/or basebandtransceivers (e.g., cellular, WLAN, GPS, Bluetooth, WiMAX, UWB, etc.)including RF circuitry, power amplifier circuits, etc., keyboardcircuitry, etc. It is noted that the keyboard circuitry may be mountedon a separate keyboard subsystem or circuit board, etc., as will beappreciated by those skilled in the art. A battery or other power supply(not shown) is also preferably secured by housing 11 for supplying powerto circuitry 148. Circuitry 148 may also comprise audio circuitry, whichincludes a microphone and related microphone signal conditioning andamplification circuitry.

The general term “RF circuitry” is intended to encompass not onlycommunication circuitry but also any other circuitry and/orinterconnection that produces electromagnetic emission. For example,processors may operate and frequencies in the range of hundredsMegahertz to several Gigahertz and may produce electromagnetic emissionat that range of frequencies. A PCB inside the device may carry signals,for example between a processor and a memory device, in that frequencyrange as well. In another example, display circuitry may also produceelectromagnetic emission at that range of frequencies. Therefore, theterm “RF circuitry” encompasses any component, circuitry andinterconnection between components that may produce electromagneticemission. Accordingly, any of the components and circuitry describedherein in relation to FIGS. 1, 2 and 3 and any of the interconnections(conductive traces) between such components may be considered “RFcircuitry”.

The device 10 may also comprise an audio output transducer 144 (e.g., aspeaker) secured in the housing 11 and connected to circuitry 148. Oneor more user input interface devices, such as a keypad (keyboard) 22, isalso preferably secured in the housing 11 and connected to circuitry148. The term keypad as used herein also refers to the term keyboard,indicating the user input devices having lettered and/or numbered keyscommonly known and other embodiments, including multi-top or predictiveentry modes. Other examples of user input interface devices include ascroll wheel 18 and a back button 19. It is appreciated that other userinput interface devices (e.g., a stylus or touch screen interface) maybe used in other embodiments.

An antenna/RF front end circuit 150 may be positioned in the lowerportion of the housing and can be formed as a pattern of conductivetraces that make an antenna circuit, which physically forms the antenna.RF front end circuitry may optionally be implemented in the antennablock 150 or in the circuit block 148. The RF output signal is input tothe circuitry block 148 for further processing.

The device 10 also comprises a plurality of auxiliary I/O devices 146.Examples of auxiliary I/O devices include a WLAN subsystem, Bluetoothsubsystem, camera subsystem for providing digital camera capabilities,GPS subsystem, flash memory card subsystem, a second audio outputtransducer (e.g., a speaker for speaker phone operation), and a cameralens for providing digital camera capabilities, an electrical deviceconnector, e.g., USB, headphone, secure digital (SD) or memory card,etc.

The device 10 also comprises a display 12, for example, a liquid crystaldisplay (LCD) secured in the housing 11 and connected to circuitry 148.A back button 19 and scroll wheel 18 can also be connected to circuitry148 for allowing a user to navigate menus, text, etc., as will beappreciated by those skilled in the art. The scroll wheel 18 may also bereferred to as a “thumb wheel” or a “track wheel”. In addition to or inthe alternative to the scroll wheel 18, the device 10 may include a userinterface apparatus such as a trackball or an optical trackpad (notshown in FIG. 2). The keypad 22 comprises a plurality of multi-symbolkeys 14 each having indicia of a plurality of respective symbolsthereon. The keypad 22 also comprises an alternate function key 15, anext key 16, a space key 17, a shift key 26, a return (or enter) key 25,a backspace/delete key 24, a send key 13, an end key 21, and aconvenience (e.g., menu) key 20 for use in placing cellular telephonecalls, as will be appreciated by those skilled in the art.

The mobile wireless communications device 10 as described herein mayadvantageously be used not only as a traditional cellular phone, but mayalso be used for sending and/or receiving data over a cellular data (3G,4G, etc.) or other network, such as Internet and email data, forexample. Of course, other keypad configurations may also be used inother embodiments. Multi-tap or predictive entry modes may be used fortyping e-mails, etc. as will be appreciated by those skilled in the art.

A block diagram illustrating the functional blocks of an examplehandheld wireless mobile communications device incorporating theelectromagnetically shielded audio system is shown in FIG. 3. The mobilecommunication device is preferably a two-way communication device havingvoice and data communication capabilities. In addition, the deviceoptionally has the capability to communicate with other computer systemsvia the Internet. Note that the mobile communications device (or mobiledevice) may comprise any suitable wired or wireless device such asmultimedia player, mobile communication device, cellular phone,smartphone, PDA, PNA, Bluetooth device, etc. For illustration purposesonly, the device is shown as a mobile device, such as a cellular basedsmartphone or so called superphone. Note that this example is notintended to limit the scope of the mechanism as the object selectionmechanism can be implemented in a wide variety of communication devices.It is further appreciated the mobile device 10 shown is intentionallysimplified to illustrate only certain components, as the mobile devicemay comprise other components and subsystems 64 beyond those shown.

The mobile device, generally referenced 10, comprises a processor 36which may comprise a baseband processor, CPU, microprocessor, DSP, etc.,optionally having both analog and digital portions. The mobile devicemay comprise a plurality of radios 34 and associated antennas 32. Radiosfor the basic cellular link and any number of other wireless standardsand Radio Access Technologies (RATs) may be included. Examples include,but are not limited to, Code Division Multiple Access (CDMA), PersonalCommunication Services (PCS), Global System for Mobile Communication(GSM)/GPRS/EDGE 3G; WCDMA; WiMAX for providing WiMAX wirelessconnectivity when within the range of a WiMAX wireless network;Bluetooth for providing Bluetooth wireless connectivity when within therange of a Bluetooth wireless network; WLAN for providing wirelessconnectivity when in a hot spot or within the range of an ad hoc,infrastructure or mesh based wireless LAN (WLAN) network; near fieldcommunications; UWB; GPS receiver for receiving GPS radio signalstransmitted from one or more orbiting GPS satellites, FM transceiverprovides the user the ability to listen to FM broadcasts as well as theability to transmit audio over an unused FM station at low power, suchas for playback over a car or home stereo system having an FM receiver,digital broadcast television, etc. The mobile device also comprisesprotocol stacks 66, which may or may not be entirely or partiallyimplemented in the processor 36. The protocol stacks implemented willdepend on the particular wireless protocols required.

The mobile device may also comprise internal volatile storage 42 (e.g.,RAM) and persistence storage 38 (e.g., ROM) and flash memory 40.Persistent storage 38 also stores applications executable by processor36 including the related data files used by those applications to allowdevice 10 to perform its intended functions. Several user-interfacedevices include trackball/touchpad/thumbwheel 44 which may comprise adepressible or otherwise operable thumbwheel/touchpad/trackball that isused for navigation, selection of menu choices and confirmation ofaction, keypad/keyboard 46 such as arranged in QWERTY fashion forentering alphanumeric data and a numeric keypad for entering dialingdigits and for other controls and inputs (the keyboard may also containsymbol, function and command keys such as a phone send/end key, a menukey and an escape key), microphone(s) 52, speaker(s) 50 and associatedaudio codec or other multimedia codecs, vibrator (not shown) foralerting a user, camera and related circuitry 56, display(s) 54 andassociated display controller. A serial/USB or other interfaceconnection 48 (e.g., SPI, SDIO, PCI, USD, etc.) provides a serial linkto a user's PC or other device. SIM/RUIM card 72 provides the interfaceto a user's SIM or RUIM card for storing user data such as address bookentries, user identification, etc.

Portable power is provided by a power pack such as the battery 70coupled to power management circuitry 68. External power is provided viaUSB power 60 or an AC/DC adapter 78 connected to the power managementcircuitry 68 which is operative to manage the charging and dischargingof the battery 70.

Operating system software executed by the processor 36 is preferablystored in persistent storage 38, or flash memory 40, but may be storedin other types of memory devices, such as a read only memory (ROM) orsimilar storage element. In addition, system software, specific deviceapplications, or parts thereof, may be temporarily loaded into volatilestorage 42, such as random access memory (RAM). Communications signalsreceived by the mobile device may also be stored in the RAM.

The processor 36, in addition to its operating system functions, enablesexecution of software applications on the device 10. A predetermined setof applications that control basic device operations, such as data andvoice communications, may be installed during manufacture. Additionalapplications (or apps) may be downloaded from the Internet and installedin memory for execution on processor 36.

When required network registration or activation procedures have beencompleted, the mobile device 10 may send and receive communicationssignals over a communications network (not shown). Signals received fromthe communications network by antenna 32 are processed by radio circuit34. Processing includes, for example, signal amplification, frequencydown conversion, filtering, channel selection, etc., and may alsoprovide analog to digital conversion, synchronization, decoding,decryption, etc. Analog-to-digital conversion of the received signalallows more complex communications functions, such as demodulation anddecoding to be performed. Signals to be transmitted are processed andtransmitted by the radio circuit 34, including digital to analogconversion, frequency up conversion, filtering, amplification andtransmission to the communication network via antenna 32.

An elevational view of a section of an example circuit boardincorporating the electromagnetically shielded audio system is shown inFIG. 4. The example circuit board layout comprises a portion of thecircuit board 120 that can be included within the mobile communicationsdevice 10 of FIGS. 1, 2 and 3. The circuit board layout comprises twoportions: a first portion comprises a microphone (MIC) 126 (surfacemounted or otherwise), EMC noise isolation circuit 124 and an RF shield122; and a second portion comprises a microphone signal conditional andamplifier circuit 132 and an RF shield 130. Although shown for clarityin FIG. 4, microphone 126 and EMC noise isolation circuit 124 may becompletely or partially obscured by RF shield 122 and amplifier circuit132 may be completely or partially obscured by RF shield 130.

The microphone 126 and related amplifier circuitry are mounted on thecircuit board 120 surrounded by RF isolation shields (“cans”), formingRF isolation compartments on the circuit board. A plurality ofmicrophone signal lines 128 are routed from the microphone 126 to theamplifier circuit 132. Each RF shield 122, 130 is electricallyconductive and may be constructed from various electrically conductivematerials, such as metal, metalized plastic, etc. and may have anysuitable shape or configuration, e.g., include sides and a top, roundwalls and a top, etc. The RF shields 122 and 130 may be solderable tocircuit board 120.

The EMC components 124 comprise passive components such as capacitors,feed through capacitors, filters and/or inductors in either a balancedand/or unbalanced configuration. EMC components 124 may be used toreduce conducted electromagnetic interference to microphone 126

Amplifier circuit 132 comprises electrical components useful forconditioning and amplifying the signal received from microphone 126.This may include active components such as audio integrated circuits(ICs), audio power amplifiers, transistors and diodes, and passivecomponents such as resistors, capacitors. Amplifier circuit 132 may alsocomprise passive components such as resistors, capacitors, filtersand/or inductors.

The RF shield 122 is a metallic or metalized housing secured to thecircuit board 120 and surrounding microphone 126, shielding microphone126 and optionally EMC components 124 from electromagnetic interference.Similarly, RF shield 130 is a metallic or metalized housing secured tothe circuit board 120 and surrounding amplifier circuitry 132, shieldingamplifier circuitry 132 from electromagnetic interference.

A sectional view of one embodiment of the electromagnetically shieldedaudio system is shown in FIG. 5. The system comprises a circuit board(e.g., printed circuit board) 80 that includes two or more layers 82. Amicrophone 96 and EMC components 98 are mounted on the circuit board 80(surface mounted or otherwise). A metal or metalized RF shield 94 ismechanically and electrically coupled to circuit board 80 and togetherwith circuit board 80 forms an interior compartment 81 surroundingmicrophone 96 and (optionally) EMC components 98. The RF shield 94provides EMI isolation for microphone 96 and (optionally) for EMCcomponents 98.

RF shield 94 comprises an opening 99 which may be located in anysuitable location on RF shield 94, e.g., top, sides, etc. An optionalacoustic tube 90 acoustically connects the RF shield 94 with an opening(e.g. hole) 86 in housing 84 of a device, e.g. mobile wirelesscommunications device 10. Acoustic tube 90 may be able to conductacoustic energy from opening 86 to opening 99 and may be referred to asan acoustic coupler. The openings 99 and 86, and acoustic tube 90, mayhave, but need not have, circular cross-sections. Moreover, openings 99and 86 may or may not have cross-sections that are similar to each otherin size or shape or both. The path of acoustic tube 90 between openings99 and 86 may be arbitrary, and as shown in FIG. 5, need not be astraight line. The acoustic tube 90 may be fastened and acousticallysealed to the RF shield 94 and housing 84 via one or more fasteningand/or sealing rings 92, 88, respectively.

The opening 99 permits acoustic energy (which may be conveyed by soundwaves) from outside the housing 84 to be channeled into compartment 81such that compartment 81 functions as an acoustic chamber 81 formicrophone 96. Once entered into acoustic chamber 81, acoustic energy(sound waves) may propagate freely throughout acoustic chamber 81. Thedimensions of acoustic chamber 81 may be selected to improve the audioperformance of microphone 96 and the corresponding audio system. Notethat the size of opening 99 in RF shield 94 may influence the resultingaudio frequency response of microphone 96.

From the point of view of RF shielding and EMC, opening 99 in RF shield94 is preferably small, for example, in the range of 1 mm in diameter,such that RF shield 94 substantially reduces penetration of externalelectromagnetic fields into compartment 81. Further, acoustic tube 90may have any suitable shape, form and profile depending on theparticular implementation. In addition, there may be any number ofopenings in the RF shield 94, any number of openings in housing 84, andany number of acoustic tubes.

A sectional view of an alternative embodiment of the electromagneticallyshielded audio system is shown in FIG. 6. In this alternativeembodiment, a microphone 110 and EMC components 112 are mounted onto acircuit board (e.g., printed circuit board) 100 having two or morelayers 102. A metal or metalized RF shield or can 108 is placed overmicrophone 110 and (optionally) EMC components 112 and is mechanicallyand electrically coupled (e.g., soldered or using pressure) to thecircuit board 100.

A flexible boot 106 made from a suitable material, such as silicon,rubber, plastic and/or other material similar thereto, is placed overthe RF shield 108 thus either partially or completely encapsulating theRF shield 108. The boot 106 may serve one or more functions, such asbeing the material that forms a flexible acoustic tube, providing shockabsorption, contributing thermal protection or improving structuralstability. Housing 104 of the device is either very close to or incontact with the boot 106 and in one embodiment may provide somepressure to seal the boot 106 to the RF shield 108.

As in the system of FIG. 5, an interior compartment 101 is createdwithin the RF shield 108 and circuit board 100 and forms an acousticchamber 101 for the microphone 110. A channel 114 for acoustic energypasses through one or more holes made in the RF shield 108, boot 106 andhousing 104. Channel 114 may be able to conduct acoustic energy from anopening in housing 104 to an opening in RF shield 108 and may bereferred to as an acoustic coupler.

In an alternative embodiment, a channel (such as channels 90 and 114)can be avoided altogether where housing 104 is in direct contact with RFshield 108 and the opening in housing 104 overlaps the opening in RFshield 108. Acoustic energy may be directed from the opening in housing104 to the opening in RF shield 108 via the overlap, which thereforeeffects an acoustic coupler.

It is appreciated that the two acoustic chamber arrangements 81 and 101of FIGS. 5 and 6 are provided for illustration purposes only. Oneskilled in the art can implement other arrangements and configurationsof the RF shield, microphone and other components to achieve the dualfunctionality of the RF shield to provide both RF shielding against EMIfor the microphone and to form an acoustic chamber for the microphone toimprove or optimize audio performance.

Dimensions of the acoustic chamber and the acoustic volume enclosedwithin the acoustic chamber may be selected to improve or optimizeacoustical properties of the audio system in which the microphone iscomprised. Dimensions of the acoustic chamber and the acoustic volumeenclosed within the acoustic chamber may be selected to achieveacoustical properties of the audio system at predefined values or withina predefined range. Examples of the acoustical properties includefrequency response, efficiency, signal to noise ratio, sound quality,background noise rejection, and voice intelligibility. The acousticvolume enclosed within the acoustic chamber may be defined, for example,as the volume of the acoustic chamber minus the volume of the componentsenclosed within the chamber. Other definitions may also be suitable.Accordingly, the size of the enclosed microphone (and optionally the EMCcomponents) may affect the design of the acoustic chamber.

For example, the required dimensions for the acoustic chamber can becalculated and simulated in accordance with the parameters andspecifications of the microphone and the requirements for the particularapplication, e.g., certification requirements for a cellular telephone,cordless phone, etc. The dimensions of the acoustic chamber may bedetermined using any suitable technique, e.g., via empiricalcalculations, simulations, trial and error, physical measurements, etc.Example constraints include volume, height, diameter, shape, length anddiameter of the acoustic tube, etc. In one embodiment, the frequencyresponse can be measured and one or more of the constraints modified.The frequency response is again measured and constraints adjusted. Thisprocess may continue until the desired frequency response is attained.

Achieving improved or optimal tuning of the acoustic chamber dimensionsmay influence the audio performance of the microphone and quality of theaudio in terms of frequency response, voice intelligibility, level ofbackground noise heard (e.g. rejection of background noise), efficiency,signal to noise ratio and sound quality. What is deemed “improved oroptimal” is generally context-dependent and may involve subjectivejudgment, and may also vary depending upon a number of factors.Consequently, although some illustrative embodiments are describedherein, the concept is not limited to those embodiments; nor is theconcept limited to any particular size, shape, volume, material or anyother constraints. In general, the concepts described herein can beapplied in a variety of devices, having a variety of geometries and avariety of components, subject to a variety of desired audiocharacteristics.

In all arrangements and configurations, the metal RF shield enclosureprovides the acoustic volume for improved or optimal microphoneperformance. The microphone in the device is physically and electricallyconnected to the circuit board, typically by soldering the metal ormetalized RF can or shield to the printed circuit board. In oneembodiment, the RF enclosure is placed over the microphone and solderedto the circuit board so as to electrically connect it to one or morelayers (e.g., at least a ground layer, that is, a layer that serves ascircuit ground, and which does not necessarily have any particularpotential with respect to the Earth) of the circuit board.

In one embodiment, the circuit board comprises a multilayer circuitboard. An illustrative connection of the components is shown in FIG. 7which illustrates the top layer 160 of an example printed circuit boardlayout comprising microphone mounting 164, solder frame 162 for the RFshield and EMC component mounting area 166. Underneath the soldering ofthe enclosure on the top surface layer is an electrical conductiveconnection with a copper area in deeper layers of the printed circuitboard. This is shown in FIG. 8 which illustrates an inner layer 170 ofthe circuit board comprising a shielding plane (or layer) 172, balancedmicrophone signal lines 174 and shielding can vias 176 along the wallsof the RF shield for contact to the ground plane. The ground plane isconnected with many vias to a deeper system ground plane layer thatcompletely covers the PCB. This provides all-around shielding for themicrophone and the EMC components. Preferably, the distance between thevias is made small, e.g., less than 5 mm, to achieve high RF isolationeffects against EMI.

FIG. 9 illustrates a second circuit board layer 180 under the top layercomprising shielding 182 for the balanced microphone signal lines thatlead to the microphone amplifier circuit 132 (FIG. 4).

The microphone is thus completely shielded from all sides, i.e.,substantially complete shielding is provided by the combination of RFshield and one or more PCB shielding layers. Optionally, the EMCcomponents are located within the RF shield enclosure physically closeto the microphone. The signal lines from the microphone pass though theEMC circuit components directly via one of the deeper layers of themultilayer PCB. They are shielded with copper traces and areas locatedin other layers of the PCB all along the path from the microphone to themicrophone input circuit. This is shown in FIG. 10 which illustrates yetanother layer 190 of the multilayer PCB comprising the balanced left andright microphone signal lines 192 to the microphone input circuit whichhave shielding 194 surrounding them. FIG. 11 illustrates the layer 200that lies below the layer of FIG. 10. This layer comprises shielding 202which provides, inter alia, a shielded channel for the balanced left andright microphone signal lines 192 (FIG. 10) to the microphone inputcircuit.

The microphone input circuit (amplifier circuit) portion of the circuitboard will now be described in more detail. The signal lines from themicrophone to the input circuit are balanced and shielded as describedsupra. Similar to the microphone, protection against EMI is provided forthe microphone signal conditioning and amplifier circuit via an RFshield enclosing the circuit. The subsequent audio signal processingstages such as signal conditioning, converting and amplification arealso enclosed by an RF shielding can with a system ground (GND) planelayer below which is located on the PCB relatively far away from themicrophone shielding to reduce coupling and interference.

The signal tracks from the microphone and EMC components are routed tothe audio signal processing stages in a deeper PCB layer. The signaltraces are placed close together to form balanced signal tracks/linesand have system GND area on the left and right side along the microphoneand audio stages to provide EMI shielding. In addition to the shieldingprovided on the same layer as the balanced microphone signal traces,shielding planes on top of and below the signals lines are providedwhich are connected using a plurality of vias to the system GND plane.This provides a complete shielding system for the microphone, the EMCcomponents, the balanced microphone signal tracks and the microphoneinput circuit.

FIG. 12 illustrates an example layer 210 of a printed circuit boardshowing the RF shielding enclosure soldering frame 212 and microphoneamplifier circuit input signal path 214.

FIG. 13 is an example layer 220 of a printed circuit board showing theshielding wall frame ground 224 and the shielding 222 for the microphonesignal path.

FIG. 14 is an example layer 230 of a printed circuit board showing theshielding for the audio shield frame ground 232. The microphone signallines are embedded left and right in GND copper planes on the samelayer. Additional GND copper planes are located in the area above and inlower PCB layers. Thus, the microphone signal lines are shielded fromall four sides.

FIG. 15 is an example layer 240 of a printed circuit board showing theground plane 242 for shielding, inter alia, the microphone signal path.

Thus, (1) the RF shielding can with the microphone and EMC componentslocated in the can, (2) the shielded microphone balanced signal path,(3) the microphone input circuit placed at a different location on thePCB and (4) the RF shielding can with the microphone input circuit,codec and other stages located therein, combine to form a completeshielded audio system. In one embodiment, no audio lines or componentsare outside these mechanical enclosures which provide the required EMIisolation an improve performance of the audio system.

Using this technique, one more embodiments of the electromagneticshielding audio system may provide benefits in a number of respects.First, the shielding can, in addition to its function as a shield, form(provide or define) an acoustic chamber together with the circuit board.The acoustic chamber may improve or optimize audio performance. Second,the electromagnetic shielding audio system may provide EMI shielding forthe microphone itself. In other words, the shielding can effectivelyperform “double-duty,” suitably serving as shielding while alsoproviding desired audio performance. Third, the shielding may offer EMIshielding from the EMC components and the signal lines. Furtheradditional benefits may also result, such as reduced cost, reduced partscount, space-saving, material-saving, simplified production steps andsimplified device design.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the mechanism. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. The term “operative to” refers to acapability of a physical component, i.e., if a component is “operativeto” perform a function, that component is capable of performing thatfunction.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the mechanism has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the mechanism in the form disclosed. As numerousmodifications and changes will readily occur to those skilled in theart, it is intended that the mechanism not be limited to the limitednumber of embodiments described herein. Accordingly, it will beappreciated that all suitable variations, modifications and equivalentsmay be resorted to, falling within the spirit and scope of themechanism. The embodiments were chosen and described in order to bestexplain the principles of the mechanism and the practical application,and to enable others of ordinary skill in the art to understand themechanism for various embodiments with various modifications as aresuited to the particular use contemplated.

It is intended that the appended claims cover all such features andadvantages of the mechanism that fall within the spirit and scope of themechanism. As numerous modifications and changes will readily occur tothose skilled in the art, it is intended that the mechanism not belimited to the limited number of embodiments described herein.Accordingly, it will be appreciated that all suitable variations,modifications and equivalents may be resorted to, falling within thespirit and scope of the mechanism.

What is claimed is:
 1. A mobile electronic device, comprising: a housinghaving an opening for entry of acoustic energy into said housing; radiofrequency ‘RF’ circuitry secured inside said housing and capable ofproducing electromagnetic emission; a circuit board secured inside saidhousing; an audio system comprising a microphone mounted on said circuitboard; a radio frequency ‘RF’ shield that is mechanically andelectrically coupled to said circuit board and surrounds saidmicrophone, said RF shield to provide some electromagnetic interference‘EMI’ isolation for said microphone from at least said electromagneticemission; an acoustic chamber surrounding said microphone, said acousticchamber enclosed within said RF shield and bounded by said circuitboard, wherein said RF shield has an opening to permit said acousticenergy to enter said acoustic chamber and wherein said acoustic energy,after entering said acoustic chamber through said opening in said RFshield, is able to propagate throughout said acoustic chamber; and anacoustic coupler to conduct said acoustic energy from said opening insaid housing to said opening in said RF shield, wherein dimensions ofsaid acoustic chamber are selected to achieve acoustical properties ofsaid audio system at predefined values or within a predefined range. 2.The mobile electronic device as claimed in claim 1, wherein saidacoustic coupler is an acoustic tube extending from said opening in saidhousing to said opening in said RF shield.
 3. The mobile electronicdevice as claimed in claim 2, wherein said acoustic tube is fastened tosaid RF shield using a fastening ring.
 4. The mobile electronic deviceas claimed in claim 2, wherein said acoustic tube is fastened to saidhousing a fastening ring.
 5. The mobile electronic device as claimed inclaim 1, wherein said acoustic coupler is a channel through a boot thatpartially or completely encapsulates said RF shield.
 6. The mobileelectronic device as claimed in claim 1, wherein said housing is indirect contact with said RF shield and said acoustic coupler is effectedthrough an overlap of said opening in said housing and said opening insaid RF shield.
 7. The mobile electronic device as claimed in claim 1,wherein said circuit board comprises a ground plane substantially undersaid RF shield for providing additional RF shielding for saidmicrophone.
 8. The mobile electronic device as claimed in claim 1,further comprising one or more electromagnetic compatibility ‘EMC’components coupled to said microphone, said one or more EMC componentsmounted on said circuit board inside said RF shield.
 9. The mobileelectronic device as claimed in claim 1, wherein said acousticalproperties include frequency response of said audio system.
 10. Themobile electronic device as claimed in claim 1, wherein said acousticalproperties include efficiency of said audio system.
 11. The mobileelectronic device as claimed in claim 1, wherein said acousticalproperties include signal to noise ratio of said audio system.
 12. Themobile electronic device as claimed in claim 1, wherein said acousticalproperties include sound quality of said audio system.
 13. The mobileelectronic device as claimed in claim 1, wherein said acousticalproperties include background noise rejection of said audio system. 14.The mobile electronic device as claimed in claim 1, wherein saidacoustical properties include voice intelligibility of said audiosystem.
 15. An electromagnetic shielded audio system, comprising: acircuit board; a microphone mounted on said circuit board; and a radiofrequency ‘RF’ shield that is mechanically and electrically coupled tosaid circuit board and surrounds said microphone, said RF shield toprovide some electromagnetic interference ‘EMI’ isolation for saidmicrophone; and an acoustic chamber surrounding said microphone, saidacoustic chamber enclosed within said RF shield and bounded by saidcircuit board, wherein said RF shield has an opening to permit acousticenergy from outside of said chamber to enter said acoustic chamber andwherein acoustic energy, after entering said acoustic chamber throughsaid opening, is able to propagate throughout said acoustic chamber, andwherein dimensions of said acoustic chamber are selected to achieveacoustical properties of said audio system at predefined values orwithin a predefined range.
 16. The electromagnetic shielded audio systemas claimed in claim 15, further comprising an acoustic coupler toconduct acoustic energy from outside of said RF shield to said openingin said RF shield.
 17. The electromagnetic shielded audio system asclaimed in claim 16, further comprising a fastening ring to connect saidacoustic coupler to said RF shield.
 18. The electromagnetic shieldedaudio system as claimed in claim 15, further comprising one or moreelectromagnetic compatibility ‘EMC’ components coupled to saidmicrophone, said one or more EMC components mounted on said circuitboard inside said acoustic chamber.
 19. The electromagnetic shieldedaudio system as claimed in claim 15, wherein said circuit boardcomprises a ground plane substantially under said RF shield to provideadditional RF shielding of said microphone.
 20. The electromagneticshielded audio system as claimed in claim 15, wherein said acousticalproperties include frequency response of said audio system.
 21. Theelectromagnetic shielded audio system as claimed in claim 15, whereinsaid acoustical properties include efficiency of said audio system. 22.The electromagnetic shielded audio system as claimed in claim 15,wherein said acoustical properties include signal to noise ratio of saidaudio system.
 23. The electromagnetic shielded audio system as claimedin claim 15, wherein said acoustical properties include sound quality ofsaid audio system.
 24. The electromagnetic shielded audio system asclaimed in claim 15, wherein said acoustical properties includebackground noise rejection of said audio system.
 25. The electromagneticshielded audio system as claimed in claim 15, wherein said acousticalproperties include voice intelligibility of said audio system.